1. Field of the Invention
The present invention relates to a video surveillance system which collects video data produced by cameras through network so as to execute concentrated monitoring at a remote monitoring station.
2. Description of the Related Art
In recent years, a variety of surveillance systems have been proposed with increased demands for disaster prevention and security maintenance.
For example, there has been currently used a video surveillance system which executes the concentrated monitoring through communication system by collecting video data in real time by means of a plurality of cameras disposed at multiple positions in various plants, construction sites, urban streets and the like and transmitting the video data over an IP network.
A conventional system uses wide-area wired communication lines as a transmission medium for network suitable for real-time pictures. However, this system has a problem that if an attempt is made to expand the system in order to expand its monitoring area after the construction of the system is completed, it takes much time and expense to construct additional wired transmission line and further, the wired transmission line cannot be placed depending on geographical condition. Therefore, it has been difficult to expand the monitoring area.
On the other hand, although a wireless LAN network constituted of a plurality of wireless nodes has been widely used recently in place of the wired IP network, the wireless LAN network has a smaller bandwidth than the wired LAN network.
For this reason, some solutions about quality of services (QoS) for securing a bandwidth for each service in this wireless LAN network have been proposed. For example, a control method which pays attention to a packet arrival interval in distribution of resources in the wireless network has been proposed (see for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-123887). However, this is expected for antenna control but not for video surveillance.
As a video surveillance system, an environmental monitoring system which relies on wireless communication through a base station has been proposed (see for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-51412).
By using a multihop network (called an ad-hoc network depending on case) which is a network configuration automatically formed by distributed wireless nodes alone without necessity of the wired infrastructure or base station, the video surveillance system can be expanded at a low cost in a short time. Further, the construction of the network is enabled even in areas in which the wired transmission line cannot be placed by using the wireless transmission. Because the multihop network has no concept of high order and low order among the nodes, which is a feature thereof, freedom degree of the system to increase/decrease of the nodes is high.
However, the current network, which is built up based on 802.11b or the like which is wireless LAN standard, is not sufficient for real-time video data transmission requiring a wide bandwidth. Further, in the multihop network, the quantity of communication among nodes such as route control information for selection of suitable route increases so that the bandwidth for use in information transmission is smaller than the conventional wireless network. Therefore, the multihop wireless network using a wireless LAN has such a problem that if the quantity of communication for other services is large in traffic within the network, insufficient bandwidth is allocated to the video data required at top priority depending on the case.